Approximately one third of lung adenocarcinomas are driven by activating mutations in the oncogene KRAS, with the most common occurring at codon 12: G12C (42%), G12V (18%) and G12D (12%) of cases respectively. Inhibitors to KRAS-G12C entered clinical trials in 2021 and have shown efficacy for the treatment of lung adenocarcinoma. Next generation inhibitors to KRAS-G12D are currently in preclinical development. KRAS mutations occur within a landscape of loss-of-function mutations in tumour suppressor genes. The most common mutations occur in tumour suppressors TP53 (40%), Serine Threonine kinase 11 (STK11) (20%), and Kelch-like ECH-associated protein 1 (KEAP1) (20%) of cases respectively. With limited clinical and preclinical data from KRAS inhibitors, it remains unknown what effect tumour heterogeneity has on response to therapy. Here we explored if loss-of-function mutations in TP53, STK11 and KEAP1 influence the response of lung adenocarcinomas to KRAS inhibitors.
To date, genetically engineered mice whereby oncogenic expression of Kras-G12D is induced in lung epithelia following the intranasal delivery of an adeno-cre virus is the “gold-standard” model in the field. These mice were crossed with mice harbouring conditional p53 or Stk11 mutations to generate KrasG12D;p53fl/fl and KrasG12D;Stk11fl/fl mice, respectively. Keap1 was then deleted using CRISPR-Cas9 gene editing in cell lines generated from lung tumours arising in KrasG12D;p53fl/fl and KrasG12D;Stk11fl/fl mice. The respective isogenic cell lines were treated with the KRAS-G12D inhibitor MRTX1133, to evaluate the impact of co-occurring mutations on treatment response. Loss of Keap1 significantly reduced sensitivity to MRTX1133 treatment in Kras/p53 and Kras/Stk11 cell lines, as assessed through cell titre glo kill curves and crystal violet assays. To assess the effect of tumour heterogeneity on KRAS-G12C inhibitor response, we have generated Kras-G12C mice. Current work exploring the impact of G12C on transformation of lung epithelia will also be presented.
Our study demonstrates that mutations in the tumour suppressor KEAP1 confer increased resistance to KRAS inhibitors. These findings have implications for the treatment of patients that harbour KEAP1 mutations. Future studies will determine the mechanism of resistance mediated by KEAP1 mutations and identify combination therapies to enhance response to KRAS inhibition in KEAP1-mutant lung cancers.